Minor compounds such as sterols, aliphatic alcohols, tocopherols, and chlorophylls in virgin olive oil from Chemlali cultivar were analyzed during the maturity process. The study concerns oils from the following three different olive growing areas of Tunisia: Sfax, Sidi Bouzid, and Enfidha. Analytical results showed that both the maturity process and the olive provenances influence the evolution of the content of these compounds.

A total of 33 virgin olive oil samples of the two main Tunisian cultivars, Chemlali and Chétoui, were characterized by their volatile compounds. The olive oil samples were obtained from olives harvested at four stages of ripeness in costal and inland farms of different geographical places. Major volatiles, mostly C6 and C5 compounds produced from linolenic and linoleic acids through the lipoxygenase cascade, were quantified by solid-phase microextraction-gas chromatography. Mathematical procedures allowed for the determination of the volatiles that not only are able to discriminate the olive oils by their olive cultivar (hexanal, E-2-hexenal, and total ketones) and ripeness (pentanal and 1-penten-3-one) but also contribute to their distinctive aroma. Finally, an electronic nose based on metal oxide sensors was checked for a rapid and at-line implementation of Tunisian olive oil varietal traceability. The classification of the samples by the sensors was explained by their sensitivity to volatiles E-2-hexanal, hexanal, 1-penten-3-one, ethanol, and Z-3-hexenol. Multivariate procedures of discriminant analysis and principal component analysis were used in the study.

Due to the importance of the stage of maturity on several olive pomological parameters and oil quality indices, and to the interest that Tunisian olive oil production has recently received, the optimal harvesting period for the main Tunisian olive cultivar, Chemlali, was assessed. For the first time, a four-season crops study, carried out in three representative geographical areas, was focused on both olive fruit pomological parameters and oil chemical composition at different stages of maturity. The stage of maturity was the factor showing the highest influence on the major part of these parameters, followed by the crop year. To guarantee a reasonable fat content and a good chemical quality of oil, in particular a harmonious acidic composition, acceptable UV absorbance, and a content high of antioxidants, unsaponifiable matter and sterols, the optimal harvesting period for Chemlali olives would appears to be between the end of November to the middle of December, which corresponds to a maturity index between 2.5 and 3.5.

-The present study reported for the first time the evolution of some minor compounds (sterols and aliphatic alcohols) composition of four Algerian olive oils according to the cultivar and the maturity stage during the season (2013/2014). Olive samples were collected during eight different harvesting dates. The studied cultivars were Chemlal, Aghenfas, Buichret and Mekki. Ten sterolic compounds, triterpene dialcohols (erythrodiol þ uvaol) and seven fatty alcohols were identified and characterized. The results showed a decreasing level of total sterols, b-sitosterol, triterpenic dialcohols, total aliphatic alcohols, tetracosanol (C24), and an increasing level of D 5 -avenasterol according to the maturity process. Linear discriminant analysis (LDA) enabled the classification of the studied varieties on the basis of analytical data and a correct classification rate of 96.5% and 88.6% was achieved using the original and cross validation method respectively. The most discriminating variables have been: cholesterol, campestanol, D 7 -stigmastenol, D 7 -avenasterol, clerosterol, alcohol C22, alcohol C25, alcohol C27.

No abstract